Trade-off between the economic and environmental impact of different decarbonisation strategies for residential buildings

German residential multi-family buildings in the 1950s-1970s age group are a relevant case study to assess the degree of certainty in meeting climate targets for the built environment. This research evaluates the contribution of traditional strategies, and whether innovative strategies perform environmentally and economically better for this purpose. We use LCA to define a benchmark for the environmental impact, expressed as lifecycle GWP, and LCC to assess the economic impact, expressed as Internal Rate of Return (IRR). The two indicators are evaluated in a Pareto optimal method. We consider combinations of strategies for the thermal envelope, the building services, and the integration of locally available renewable energy in five existing buildings. Results show that accelerating the implementation rate of traditional strategies contributes only partially to raise the degree of certainty in reaching climate targets. For this purpose, innovative building services strategies as well as the extensive integration of local energy generation from renewable sources is required, even if the GWP reduction target of electricity from the main grid is met. The use of renewable energy has a much bigger impact on the overall GWP balance than the choice between a standard renovation and a minimal renovation of the building envelope. IRR tends to sink with GWP. We conclude that a regulated benchmark for the environmental lifecycle impact of residential building projects will help to introduce the trade-off assessment necessary to identify economically sustainable strategies that increase the level of certainty in meeting climate targets.